You're not actually opening the JPG as a Raw file, your just opening the JPG file in the Adobe Camera Raw converter (ACR).
A JPG has all the image settings locked in.
Even so, opening the JPG in ACR gives you some ability to adjust things like white balance, contrast, exposure, etc.
A RAW image is really the Raw data file created by the camera.
It has a larger dynamic range so you can compensate for a under or over exposed image within limits.
Adjustments like white balance, contrast, saturation, etc., are completely adjustable and not locked in like a JPG.
I think the biggest advantage to opening a JPG in ACR is adjusting for blown out highlights.
You can't bring back what isn't there but can minimize the problem in some images.